Zinc is a metal element that is essential for life, but is toxic when present in excess. Cells therefore rely on mechanisms to maintain a relatively constant intracellular level of zinc despite fluctuations in the extracellular medium. To ensure that zinc levels are maintained at an optimal level for cell metabolism, the expression of genes necessary for zinc transport or zinc storage is often dependent upon cellular zinc levels. Although such changes in gene expression are central to zinc homeostasis, the identity of the factors that sense intracellular zinc levels and mediate these changes is largely unknown. The long-term goal of our research is to understand how eukaryotic cells sense and regulate intracellular zinc levels. To identify proteins that sense zinc, we have taken advantage of the versatile genetics of Schizosaccharomyces pombe. Using this model system we have isolated a novel factor that is required for zinc-dependent regulation of gene expression. This factor, designated Loz1, contains a double C2H2-type zinc finger domain that is essential for zinc-dependent regulation of gene expression. This proposal describes a combined molecular, genetic and biochemical approach to determine how Loz1 is regulated by zinc. Specifically, we will address whether Loz1 directly senses zinc levels, and whether this requires the double C2H2-type zinc finger domain.